1. Technical Field
The present disclosure relates to a failure detection system and failure detection method configured to detect a failure in a sound collection element.
2. Description of the Related Art
When collecting a sound of interest such as a voice, a sound collection technology with a high SN ratio is strongly desired so as not to collect an unnecessary sound such as a noise, an interference sound, or the like. In order to achieve such a technology, it is considered that signal processing using a sound collection device (microphone array device) configured of a plurality microphone elements is effective.
As an example of the signal processing using the microphone array device, there is a method (delay-sum method) in which the directivity of a voice is formed in a predetermined direction by adding a different delay time for each microphone element to the audio signal collected by each microphone element, and then summing the audio signals. In this delay-sum method, it is necessary to make the beam width of the directivity be narrow in order to obtain a directivity in the low frequency while it is easy to control the directivity in the signal processing device that performs the signal processing. Therefore, the number of arrayed microphone elements increases, which results in the increase of the size of a microphone array device.
In addition, other than the delay-sum method, there is a method (delay difference method) in which the directivity of a voice is formed in a predetermined direction by subtracting audio signals after adding a delay time to the audio signal and then forming a blind spot (sensitivity is low) in the noise direction. The microphone array device using such a delay difference method automatically forms the directivity according to the surrounding noise environment, and thus, it is called an adaptive microphone array device.
A principle of forming the directivity in the adaptive microphone array device is as follows (for example, refer to following literature: Acoustic system and digital principle, P190, by Taiga, Yamazaki, and Kaneda, Corona Publishing Co., Ltd. Mar. 25, 1995. (Griffith-Jim type adaptive microphone array device). The adaptive microphone array device geometrically calculates a time difference of a collection time in which the audio signal in a target direction is collected in each microphone using an arrival direction of an objective audio signal and an array position of each microphone. The adaptive microphone array device adds a delay amount which corresponds to the time difference between the audio signal collected by each microphone. In this way, phases of the audio signals are synchronized in a target direction. In addition, the adaptive microphone array device erases the audio signal in the target direction by getting a difference between the phase-synchronized audio signal and the adjacent audio signal, and obtains signals (noise signals) that include only multiple noises of adjacent numbers. The adaptive microphone array device can obtain the audio signal in which the surrounding noises are suppressed and the directivity in the target direction is formed by causing each noise signal to pass through an adaptive filter, and then, subtracting the output of the adaptive filter from the delay output of a first microphone.
In the adaptive microphone array device in which the delay difference method is used, in a case where characteristics deteriorate or a failure occurs in any of the microphone elements, it influences the difference result of the audio signal. Then, the audio signal in which the surrounding noises are suppressed in the target direction cannot be obtained, and thus, the accuracy of forming the directivity deteriorates.
For this reason, in the adaptive microphone array device in which the delay difference method is used, it is necessary to check whether or not the characteristics of all the microphone elements are uniform by monitoring the characteristics of the microphone element in use or a circuit for amplifying the audio signal collected by the microphone element.
However, when it is desired to form directivity in an arbitrary direction using a microphone array device, in the adaptive microphone array device in which the delay difference method is used, since it is assumed that the characteristics of all the microphone elements are uniform at the time point before actual using, it is not considered that the characteristics deteriorate or that a failure may occur in the microphone element at the time of actual using. Therefore, for example, at the time of actual use in a case where characteristics deteriorate or there is failure in the microphone element, it can be considered that the accuracy of forming the directivity of a voice in a specific direction from the microphone array device deteriorates.